Method for polymerizing contact lenses

ABSTRACT

A method for photopolymerizing a monomer mixture to form a lens involves charging to a mold a monomer mixture including lens-forming monomers, and exposing the monomer mixture in the mold to a light source including light in the visible region of the spectrum. The method is useful for monomer mixtures that include a UV-absorbing compound and/or a tinting agent. Preferably, the monomer mixtures include a polymerization initiator including a phosphine oxide moiety.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for photopolymerizing amonomer mixture to form a lens, wherein the monomer mixture may includea UV-absorbing compound and a tint and is exposed to a light sourceincluding light in the visible region of the spectrum.

[0002] Lenses such as contact lenses or intraocular lenses may include aUV absorbing agent in the lens to absorb light in the ultraviolet regionof the spectrum, more particularly, to absorb light in the region ofabout 200 to 400 nm and, especially, about 290 to 400 nm. RepresentativeUV absorbing materials for such lens applications are described in U.S.Pat. Nos. 4,304,895 (Loshaek), 4,528,311 (Beard et al.) and 4,719,248(Bambury et al.).

[0003] Such lenses may also include a tint. The tint may be relativelyrich in hue, so as to change or at least enhance the color of the iriswhen the lens is placed thereon. Alternately, the tint may be relativelylight in hue, so that it does not change or enhance the color of theiris but does facilitate handling of the lens by a user; arepresentative “visibility tint” for contact lenses is described in U.S.Pat. No. 4,997,897 (Melpolder).

[0004] Generally, such lenses are formed by free radical polymerizationof a monomer mixture including desired lens-forming monomers, usually inthe presence of heat (thermal polymerization) or a light source(photopolymerization). One particular method for producing contactlenses involves thermal polymerization of the initial monomeric mixturein tubes in a heated water bath to provide rod-shaped articles, whichrods are then cut into buttons, the buttons then being lathed intocontact lenses; such methods for forming lenses including a UV absorbingagent are illustrated in the aforementioned U.S. Pat. Nos. 4,304,895(Loshaek) and 4,528,311 (Beard et al.). Other methods involve castingthe lenses directly in molds, wherein the monomer mixture is charged tothe mold and polymerized by exposure to ultraviolet radiation.

[0005] Among photopolymerization processes, UV curing (i.e., exposure ofthe monomer mixture to radiation mainly in the ultraviolet region) ofthe monomer mixtures has proved very effective. However, for lensesincluding a UV absorbing agent, problems are encountered when attemptingto cure the monomer mixtures since this agent absorbs UV light, thusdiminishing the amount of UV light available to effect polymerizationand resulting in ineffective or uneven curing of the monomer mixture.

[0006] It is also possible to effect photopolymerization using a lightsource also including light in the visible region of the spectrum,although light in this region is generally less efficient in effectingpolymerization of conventional lens-forming monomer mixtures than UVcuring. U.S. Pat. No. 4,719,248 (Bambury) reports successfulpolymerization of contact lens compositions including a UV absorbingagent by exposure of the monomer mixture to visible light. However, ithas been found that the methods illustrated in the Bambury patent couldnot effectively polymerize monomer mixtures for contact lenses thatincluded, in addition to the UV absorbing agent, a tinting agent.

[0007] Accordingly, it would be desirable to provide a method wherebylenses including both a UV absorbing agent and a tinting agent can beeffectively photopolymerized by free radical polymerization. The presentinvention provides such a method and solves the aforementioned problems.

SUMMARY OF THE INVENTION

[0008] The invention provides a method for photopolymerizing a monomermixture to form a lens comprising charging to a mold a monomer mixtureincluding lens-forming monomers, and exposing the monomer mixture in themold to a light source including light in the visible region of thespectrum. The method is useful for monomer mixtures that include aUV-absorbing compound and a tinting agent. Preferably, the monomermixtures include a polymerization initiator including a phosphine oxidemoiety.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0009] The monomer mixtures employed in the invention includeconventional lens-forming monomers, UV absorbing agents and tintingagents.

[0010] The lens-forming monomers are monomers that are polymerizable byfree radical polymerization, generally including an activatedunsaturated radical, and most preferably an ethylenically unsaturatedradical. (As used herein, the term “monomer” denotes relatively lowmolecular weight compounds that are polymerizable by free radicalpolymerization, as well as higher molecular weight compounds alsoreferred to as “prepolymers”, “macromonomers”, and related terms.)

[0011] An especially preferred class of lens-forming monomers are thosethat form hydrogel copolymers. A hydrogel is a crosslinked polymericsystem that can absorb and retain water in an equilibrium state.Accordingly, for hydrogels, the monomer mixture will typically include ahydrophilic monomer. Suitable hydrophilic monomers include: unsaturatedcarboxylic acids, such as methacrylic and acrylic acids; acrylicsubstituted alcohols, such as 2-hydroxyethylmethacrylate and2-hydroxyethylacrylate; vinyl lactams, such as N-vinyl pyrrolidone; andacrylamides, such as methacrylamide and N,N-dimethylacrylamide.

[0012] Another preferred class of lens-forming monomers are those thatform silicone hydrogel copolymers. Such systems include, in addition toa hydrophilic monomer, a silicone-containing monomer. One suitable classof silicone containing monomers include known bulky, monofunctionalpolysiloxanylalkyl monomers represented by Formula (I):

[0013] wherein:

[0014] X denotes —COO—, —CONR⁴—, —OCOO—, or —OCONR⁴— where each where R⁴is H or lower alkyl; R³ denotes hydrogen or methyl; h is 1 to 10; andeach R² independently denotes a lower alkyl or halogenated alkylradical, a phenyl radical or a radical of the formula

—Si(R ⁵)₃

[0015] wherein each R⁵ is independently a lower alkyl radical or aphenyl radical. Such bulky monomers specifically includemethacryloxypropyl tris(trimethylsiloxy)silane, pentamethyldisiloxanylmethylmethacrylate, tris(trimethylsiloxy) methacryloxy propylsilane,methyldi(trimethylsiloxy)methacryloxymethyl silane,3-[tris(trimethylsiloxy)silyl] propyl vinyl carbamate, and3-[tris(trimethylsiloxy)silyl] propyl vinyl carbonate.

[0016] Another suitable class are multifunctional ethylenically“end-capped” siloxane-containing monomers, especially difunctionalmonomers represented Formula (II):

[0017] wherein:

[0018] each A′ is independently an activated unsaturated group;

[0019] each R′ is independently are an alkylene group having 1 to 10carbon atoms wherein the carbon atoms may include ether, urethane orureido linkages therebetween;

[0020] each R⁸ is independently selected from monovalent hydrocarbonradicals or halogen substituted monovalent hydrocarbon radicals having 1to 18 carbon atoms which may include ether linkages therebetween, and

[0021] a is an integer equal to or greater than 1. Preferably, each R⁸is independently selected from alkyl groups, phenyl groups andfluoro-substituted alkyl groups. It is further noted that at least oneR⁸ may be a fluoro-substituted alkyl group such as that represented bythe formula:

—D′—(CF₂)_(S) —M′

[0022] wherein:

[0023] D′ is an alkylene group having 1 to 10 carbon atoms wherein saidcarbon atoms may include ether linkages therebetween;

[0024] M′ is hydrogen, fluorine, or alkyl group but preferably hydrogen;and

[0025] s is an integer from 1 to 20, preferably 1 to 6.

[0026] With respect to A′, the term “activated” is used to describeunsaturated groups which include at least one substituent whichfacilitates free radical polymerization, preferably an ethylenicallyunsaturated radical. Although a wide variety of such groups may be used,preferably, A′ is an ester or amide of (meth)acrylic acid represented bythe general formula:

[0027] wherein X is preferably hydrogen or methyl, and Y is —O— or —NH—.Examples of other suitable activated unsaturated groups include vinylcarbonates, vinyl carbamates, fumarates, fumaramides, maleates,acrylonitryl, vinyl ether and styryl. Specific examples of monomers ofFormula (II) include the following:

[0028] wherein:

[0029] d, f, g , h and k range from 0 to 250, preferably from 2 to 100;and

[0030] M′ is hydrogen or fluorine.

[0031] A further suitable class of silicone-containing monomers includesmonomers of the Formulae (IIIa) and (IIIb):

(IIIa) E′(*D*A*D*G)_(a) *D*A*D*E′; or

(IIIb) E′(*D*G*D*A)_(a) *D*G*D*E′;

[0032] wherein:

[0033] D denotes an alkyl diradical, an alkyl cycloalkyl diradical, acycloalkyl diradical, an aryl diradical or an alkylaryl diradical having6 to 30 carbon atoms;

[0034] G denotes an alkyl diradical, a cycloalkyl diradical, an alkylcycloalkyl diradical, an aryl diradical or an alkylaryl diradical having1 to 40 carbon atoms and which may contain ether, thio or amine linkagesin the main chain;

[0035] * denotes a urethane or ureido linkage;

[0036] a is at least 1;

[0037] A denotes a divalent polymeric radical of the formula:

[0038] wherein:

[0039] each R^(Z) independently denotes an alkyl or fluoro-substitutedalkyl group having 1 to 10 carbon atoms which may contain ether linkagesbetween carbon atoms;

[0040] m′ is at least 1; and

[0041] p is a number which provides a moiety weight of 400 to 10,000;

[0042] each E′ independently denotes a polymerizable unsaturated organicradical represented by the formula:

[0043] wherein:

[0044] R₂₃ is hydrogen or methyl;

[0045] R₂₄ is hydrogen, an alkyl radical having 1 to 6 carbon atoms, ora —CO—Y—R₂₆ radical wherein Y is —O—, —S— or —NH—;

[0046] R₂₅ is a divalent alkylene radical having 1 to 10 carbon atoms;R₂₆ is a alkyl radical having 1 to 12 carbon atoms; X denotes —CO— or—OCO—; Z denotes —O— or —NH—; Ar denotes an aromatic radical having 6 to30 carbon atoms; w is 0 to 6; x is 0 or 1; y is 0 or 1; and z is 0 or 1.

[0047] A specific urethane monomer is represented by the following:

[0048] wherein m is at least 1 and is preferably 3 or 4, a is at least 1and preferably is 1, p is a number which provides a moiety weight of 400to 10,000 and is preferably at least 30, R₂₇ is a diradical of adiisocyanate after removal of the isocyanate group, such as thediradical of isophorone diisocyanate, and each E″ is a group representedby:

[0049] Other silicone-containing monomers include thesilicone-containing monomers described in U.S. Pat. Nos. 5,034,461,5,610,252 and 5,496,871, the disclosures of which are incorporatedherein by reference. Other silicone-containing monomers are well-knownin the art.

[0050] In the case of hydrogels, either the silicone-containing monomeror the hydrophilic monomer may function as a crosslinking agent (acrosslinker being defined as a monomer having multiple polymerizablefunctionalities) or a separate crosslinker may be employed.

[0051] The monomer mixtures include a UV-absorbing agent, defined as anagent that, when incorporated in the final lens, is capable of reducingat least 70% percent of light in the region of 200 to 400 nm, morepreferably at least 70% of light in the region of 320 to 400 nm and atleast 90% of light in the region of 290 to 320 nm. The invention issuitable for monomer mixtures including any conventional UV absorbingagent. One general class of such agents are non-polymerizable absorberssuch as 2,2-drihydoxy-4,4-dimethoxy-benzophenone, and2,2-dihydoxy-4-methoxy-benzophenone. Preferred, however, arepolymerizable UV absorbing agents that include an activated unsaturatedgroup that is reactive with the lens-forming monomers, whereby the UVabsorbing agent is copolymerized with the lens-forming monomers.Representative polymerizable UV absorbing materials for such lensapplications are described in U.S. Pat. Nos. 4,304,895 (Loshaek),4,528,311 (Beard et al.), 4,716,234 (Dunks et al.), 4,719,248 (Bamburyet al.), 3,159,646 (Milionis et al.) and 3,761,272 (Manneus et al.), thedisclosures of which are incorporated herein by reference Specificexamples include: benzotriazole-containing monomers such as2-(2′-hydroxy-5′-methacrylamidophenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-5′-methacrylamidophenyl)-5-methoxybenzotriazole,2-(2′-hydroxy-5′-methacryloxypropyl-3′-t-butyl-phenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-5′-methacryloxyethylphenyl)benzotriazole,2-(2′-hydroxy-5′-methacryloxypropylphenyl)benzotriazole; and thepolymerizable benzophenones described in U.S. Pat. No. 4,304,895.

[0052] The monomer mixtures may also include a tinting agent, defined asan agent that, when incorporated in the final lens, imparts some degreeof color to the lens. The invention is applicable to conventionaltinting agents known in the art, including non-polymerizable agents, orpolymerizable agents that include an activated unsaturated group that isreactive with the lens-forming monomers. One preferred example of thislatter class is the compound1,4-bis(4-(2-methacryloxyethyl)phenylamino)anthraquinone, a bluevisibility-tinting agent disclosed in U.S. Pat. No. 4,997,897.

[0053] As mentioned, photopolymerization of monomer mixtures to formlenses by UV curing has proved very effective, however, for lensesincluding a UV absorbing agent, ineffective or uneven curing isencountered since this agent absorbs UV light. The invention provides amethod whereby lenses including both a UV absorbing agent and a tintingagent can be effectively photopolymerized by free radicalpolymerization.

[0054] More specifically, it was found that use of an initiator thatincludes a phosphine oxide moiety permitted satisfactory curing ofmonomer mixtures by photopolymerization to form lenses. Accordingly, itis preferred that the initial monomer mixtures include a phosphineoxide-containing initiator. The phosphine oxide moiety may berepresented by the formula:

[0055] Preferred initiators include the following phosphineoxide-containing radical:

[0056] where n is zero or one, and preferably one.

[0057] Representative compounds with this phosphine oxide-containingmoiety are of the formula:

[0058] wherein Ar and Ar′ are independently an optionally substitutedaromatic radical, and R is an alkyl or optionally substituted aromaticradical, and n is zero or one and preferably one. Specific examples ofsuch phosphine oxide-containing compounds include:bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (TMBPPO);bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (DMBAPO);2,4,6-trimethylbenzyldiphenyl phosphine oxide; and2,4,6-trimethylbenzyoyl diphenylphosphine oxide (MAPO). Commerciallyavailable initiator systems with these compounds include: Irgacure-819™initiator, based on TMBPPO (Ciba Specialty Chemicals); Irgacure- 1700™initiator, including DMBAPO at about 25 wt % (Ciba Specialty Chemicals);Irgacure-1800™ initiator, including DMBAPO at about 25 wt % (CibaSpecialty Chemicals); MAPO (Ciba Specialty Chemicals); and Lucirin TPO™initiator, based on 2,4,6-trimethylbenzyldiphenyl phosphine oxide(BASF).

[0059] Generally, the monomer mixtures is charged to a mold, and thensubjected to light to effect curing of the monomer mixture in the mold.Various processes are known for curing a monomeric mixture in theproduction of contact lenses, including spincasting and static casting.Spincasting methods involve charging the monomer mixture to a mold, andspinning the mold in a controlled manner while exposing the monomermixture to light. Static casting methods involve charging the monomermixture between two mold sections, one mold section shaped to form theanterior lens surface and the other mold section shaped to form theposterior lens surface, and curing the monomer mixture by exposure tolight. Such methods are described in U.S. Pat. Nos. 3,408,429,3,660,545, 4,113,224, 4,197,266, and 5,271,875.

[0060] For the present invention, any light source may be used so longas it provides light in the visible region of the spectrum, andespecially 400 to 500 nm. It is noted, however, that in some cases itmay be desirable to filter out light in the ultraviolet region of thespectrum, especially light in the region of 300 to 400 nm; in somecases, exposure to light in this region may lead to undesired “warping”of the lens or “curling” at edges of the lens. Accordingly, although thelight source does not need to provide light exclusively in the visibleregion of the spectrum, according to a distinct preferred embodiment themonomer mixture is exposed to light predominantly in the visible regionof the spectrum. This may be accomplished either by selection of anappropriate light source relatively specific to visible light, or byusing a light source providing a broad spectrum of light and filteringout UV radiation impinging on the monomer mixture.

[0061] The following examples illustrate various preferred embodiments.The following nomenclature is used in the description of experimentalprocedures:

[0062] F₂D₂₀—a polysiloxanediol-based fumarate prepolymer of Formula(IIc) endcapped with t-butylamine (derived from apolydimethylsiloxanediol, fumaryl chloride and t-butylamine according toU.S. Pat. No. 5,420,324) and described more fully in Synthesis C below.

[0063] ID2S4H—a polyurethane-based prepolymer endcapped with2-methacryloxyethyl (derived from isophorone diisocyanate, diethyleneglycol, a polydimethylsiloxanediol, and 2-hydroxyethyl methacrylateaccording to U.S. Pat. No. 5,034,561) and described more fully inSynthesis A below.

[0064] ID3S4H—a polyurethane-based prepolymer endcapped with2-methacryloxyethyl (derived from isophorone diisocyanate, diethyleneglycol, a polydimethylsiloxanediol, and 2-hydroxyethyl methacrylateaccording to U.S. Pat. No. 5,034,561) and described more fully inSynthesis B below.

[0065] TRIS—3-methacryloxypropyl tris(trimethylsiloxy)silane

[0066] DMA—N,N-dimethylacrylamide

[0067] IMVT—1,4-bis(4-(2-methacryloxyethyl)phenylamino)anthraquinone(Example 1i of U.S. Pat. No. 4,997,897), a blue visibility-tinting agent

[0068]UVAgent—2-(2-hydroxy-5-methacrylamidophenyl)-5-methoxybenzotriazole(Example 4 of U.S. Pat. No. 4,719,248)

[0069] TXN—thioxoanthen-9-one

[0070] MDEA—N-methyldiethanolamine

[0071] Darocur-1173™—a commercial acetophenone-based initiator (CibaSpecialty Chemical), based on 2-hydroxy-2-methyl-phenylpropan- 1-one

[0072] Irgacure-184™—(I-184) a commercial acetophenone-based initiator(Ciba Specialty Chemical), based on 1-hydroxycyclohexyl phenyl ketone

[0073] Irgacure-784™—(I-784) a commercial titanocene-based initiator(Ciba Specialty Chemical)

[0074] Irgacure-819™—(I-819) a commercial initiator based onbis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (Ciba SpecialtyChemical),

[0075] Irgacure-1700™—(I-1700) a commercial initiator based onbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (about 25wt %) and the Darocur-1173™ acetophenone-based initiator (Ciba SpecialtyChemical)

[0076] Irgacure-1800™—(I- 1800) a commercial initiator based onbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (about 25wt %) and the Irgacure-184™ acetophenone-based initiator (Ciba SpecialtyChemical)

[0077] Synthesis A

[0078] Preparation of a polydimethylsiloxane-based polyurethanepolymer—(ID2S4H)

[0079] A dry 3-neck, 1000 mL round bottom flask was connected to anitrogen inlet tube and a reflux condenser linked. Then, isophorone(16.916 g, 0.0761 mole), diethylene glycol (4.038 g, 0.0380 mole),dibutyl tin dilaurate (0.383 g) and 140 mL of methylene chloride wereadded into the flask all at once and the contents were refluxed. After16 hours, the amount of isocyanate was determined and decreased to 47.0%by titration. Then α,ω-bis(4-hydroxybutyl)polydimethylsiloxane (102.56g, 0.02536 mole) was added into the flask. Refluxing was continued for33 hours, and the amount of isocyanate was decreased to 14.1% of theoriginal by titration. The contents were then cooled to ambienttemperature. 2-Hydroxyethyl methacrylate (2.2928 g) and 1,1′-bi-2-phenol(0.0129 g) were then added and the contents were stirred at ambientuntil isocyanate peak at 2267 cm⁻¹ disappeared from IR spectrum of theproduct. The solvent was then stripped under reduced pressure to yieldthe product.

[0080] Synthesis B

[0081] Preparation of a polydimethylsiloxane-based polyurethanepolymer—(ID3S4H)

[0082] The procedure in Example 1 was followed except that the molarratios of ingredients was varied. Specially, the amounts of ingredientsin the early synthesis step were: isophorone diisocyanate (10.425 g,0.04799 mole) and diethylene glycol (2.5469 g, 0.024 mole); and in thesubsequent synthesis step, α,ω-bis(4-hydroxybutyl) polydimethylsiloxane(74.22 g, 0.01799 mole), and 2-hydroxyethyl methacrylate (1.8376 g).

[0083] Synthesis C

[0084] Preparation of a polydimethylsiloxane-based fumarate prepolymerend-capped with t-butylamine (F₂D₂₀)

[0085] A 3-neck, 500 mL round bottom flask was connected to a nitrogeninlet tube and a reflux condenser was linked in series to a potassiumhydroxide tube and a sodium hydroxide solution. Fumaryl chloride (12.56g, 0.082 mole), α,ω-bis(4-hydroxybutyl) polydimethylsiloxane of Mn 1595(59.81 g, 0.0375 mole) and 250 mL of anhydrous methylene chloride wereadded to the flask. The contents were refluxed under nitrogen purging.After 18 hours, it was found that the OH groups were gone by analyzingan aliquot by high resolution NMR. The unreacted fumaryl chloride andthe solvent were stripped under vacuum. Next, 50 mL of methylenechloride was added and the mixture cooled to 0-5° C. Then, t-butylamine(11.67 g, 0.1595 mole) in 250 mL of methylene chloride was added slowlyto maintain a low temperature. The mixture was kept at room temperaturewhile stirring overnight. The ammonium salt was filtered and the mixturewashed with aqueous sodium bicarbonate two times and then with wateruntil neutral. The product was dried with magnesium sulfate and themethylene chloride was stripped. This crude product (64.5 g) was thenredissolved in 130 mL of methylene chloride and passed through a silicagel column. The first 195 mL was collected then the column was elutedwith 65 mL of methylene chloride. The final combined 260 mL eluent wasrotevaporated and vacuum dried at 80° C. to give to give 62.3 g product.The prepolymer was characterized by IR, NMR and size exclusionchromatography (SEC). IR (cm⁻¹):3325, 2962, 1727, 1644, 1541, 1456,1412, 1365, 1297, 1257, 1222, 1159, 1010, 963 and 786; 200 Mhz H—NMR(ppm) 0.00, 0.56 (t), 1.39 (s,) 1.40 (m) 1.69 (m), 4.17 (t), 5.70(broad), 6.77 (m); SEC (by polystyrene standard) gave Mn of 2593, Mw3,887; polydispersity 1.50.

[0086] Preparation of monomer mixtures

[0087] A first series of monomer mixtures, suitable for providingsilicone hydrogel contact lenses, were prepared by mixing the followingcomponents:

[0088] Mixture 1A—F₂D₂₀ (20 parts by weight (pbw)); TRIS (40 pbw), DMA(40 pbw); hexanol solvent (20 pbw); and Darocur-1173 initiator (0.5 pbw)

[0089] Mixture 1B—F₂D₂₀ (20 parts by weight (pbw)); TRIS (40 pbw), DMA(40 pbw); hexanol solvent (20 pbw); and UVAgent (0.5 pbw)

[0090] Mixture 1C—F₂D₂₀ (20 parts by weight (pbw)); TRIS (40 pbw), DMA(40 pbw); hexanol solvent (20 pbw); UVAgent (0.5 pbw); and IMVT (150ppm)

[0091] A second series of monomer mixtures, suitable for providingsilicone hydrogel contact lenses, were prepared by mixing the followingcomponents:

[0092] Mixture 2A—ID2S4H (50 parts by weight (pbw)); TRIS (20 pbw), DMA(30 pbw); hexanol solvent (20 pbw); and Darocur-1173 initiator (0.5 pbw)

[0093] Mixture 2B—ID2S4H (50 parts by weight (pbw)); TRIS (20 pbw), DMA(30 pbw); hexanol solvent (20 pbw); and UVAgent (0.5 pbw)

[0094] Mixture 2C—ID2S4H (50 parts by weight (pbw)); TRIS (20 pbw), DMA(30 pbw); hexanol solvent (20 pbw); UVAgent (0.5 pbw); and IMVT (150ppm)

[0095] General preparation of hydrogel films

[0096] Monomer mixtures were cured into films by placing the mixturebetween two silane-treated glass plates and exposing to a light sourcefor 1 hour. Cured films were released from the plates and extracted withisopropanol, then heated in boiling water. Films were equilibrated inborate buffered saline before characterization.

COMPARATIVE EXAMPLES

[0097] To Mixtures 1B and 2B was added 0.5% of Darocur-1173 initiator.Then, these mixtures, along with Mixtures 1A and 2A, were cured under UVlight (4000 μW) according to the procedure described above. Mixtures 1Aand 2A, containing neither a UV absorbing agent nor a tinting agent,were fully cured. However, for Mixtures 1B and 2B, containing a UVabsorbing agent but no tinting agent, the mixtures became very viscousbut were not cured.

COMPARATIVE EXAMPLES

[0098] To Mixtures 1B, 1C, 2B and 2C were added 0.2 wt % TXN and 0.4 wt% MDEA. Then, these mixtures were cured under visible light (about 16mW) in a nitrogen atmosphere according to the procedure described above.Mixtures 1B and 2B, containing a UV absorbing agent but no tintingagent, were cured, although the films were curly. These results areconsistent with the experiments reported in U.S. Pat. No. 4,719,248.However, for Mixtures 1C and 2C, containing both the UV absorbing agentand the tinting agent, the mixtures became very viscous but were notcured.

COMPARATIVE EXAMPLES

[0099] To Mixtures 1B, 1C, 2B and 2C were added 0.2 wt % camphor quinoneand 0.4 wt % MDEA. Then, these mixtures were cured under visible light(about 16 mW) in a nitrogen atmosphere according to the proceduredescribed above. Mixtures 1B and 2B, containing a UV absorbing agent butno tinting agent, were cured, although the films were curly. However,for Mixtures 1C and 2C, containing both the UV absorbing agent and thetinting agent, the mixtures stayed fluid.

COMPARATIVE EXAMPLES

[0100] To Mixtures 1C and 2C (containing both a UV-absorbing agent and atinting agent) was added Irgacure-784 initiator at amounts of 0.25, 0.5,0.75 and 1.0 wt %. Then, these mixtures were exposed to visible light ina nitrogen atmosphere according to the procedure described above. Themixtures stayed fluid.

EXAMPLES 1 AND 2

[0101] Irgacure-1700 initiator was added to Mixtures 1C and 2C(containing both a UV-absorbing agent and a tinting agent) at amounts of1.0, 2.0, 3.0 and 4.0 weight percent. Additionally, Irgacure-1800initiator was added to Mixtures 1C and 2C at amounts of 1.0, 2.0, 3.0and 4.0 weight percent. Both of these initiator systems include about 25weight percent ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Then,this series of mixtures was cured under visible light in a nitrogenatmosphere according to the procedure described above. Hydration andequilibration in borate buffered saline yielded hydrogel films. Thehydrogel films showed some curliness at edges of the films.

EXAMPLES 3 AND 4

[0102] Irgacure-819 initiator was added to Mixtures 1C and 2C(containing both a UV-absorbing agent and a tinting agent) at amounts of0.25, 0.5, 0.75 and 1.0 weight percent. This initiator system is basedon bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide. Then, this seriesof mixtures was cured under visible light in a nitrogen atmosphereaccording to the procedure described above. The monomer mixtures werefully cured to form films. The films were initially somewhat yellow inappearance, but upon hydration and equilibration in borate bufferedsaline, the hydrogel films appeared green. The hydrogel films showedsome curliness at edges of the films.

EXAMPLES 5 AND 6

[0103] Irgacure-819 initiator was added to Mixtures 1C and 2C(containing both a UV-absorbing agent and a tinting agent) at 0.75weight percent. This initiator system is based onbis(2,4,6-trimethylbenzoyl) phenylphosphine oxide. Then, this series ofmixtures was cured under visible light as in Examples 3 and 4, exceptthat a glass plate coated with a UV-absorbing agent was placed betweenthe light source and the monomer mixture to be cured, such that thiscoated plate was able to filter substantially all light below 400 nm.The monomer mixes were fully cured to form films. Upon hydration andequilibration in borate buffered saline, the hydrogel films exhibited nocurliness.

EXAMPLE 7

[0104] A series of monomer mixtures prepared as in Examples 5 and 6 wasused to cast contact lenses. The monomer mixtures were placed on themolding surface of a first plastic mold section, shaped to provide ananterior contact lens surface, and a second plastic mold section havinga molding surface shaped to provide a posterior contact lens surface wasplaced on the first mold section, the monomer mixture being contained inthe mold cavity formed between these two molding surfaces. This assemblywas then subjected to visible light source for 1 hour. The two moldsections were separated, the lenses were released from the mold sectionin isopropanol, then heated in boiling water. The lenses wereequilibrated in borate buffered saline before characterization,resulting in hydrogel contact lenses having good optical quality.

EXAMPLE 8

[0105] Hydrogel films from Example 1 (based on Mixture 1C with 1.0weight percent Irgacure-1700 initiator, and based on Mixture 1C with 1.0weight percent Irgacure-1800 initiator), the films having a thickness of180 microns, were subject to UV-VIS absorption measurements. Both setsof films had analogous light transmittance. Wavelength (nm)Transmittance (% T) 400-800 92 200-400 2.7 320-400 (UVA) 6.5 320-290(UVB) 0.4 290-200 (UVC) 0.2

EXAMPLES 9-18

[0106] Various initiators were added to Monomer Mixture 1C, and hydrogelfilms were cured under a visible light source and processed according tothe general procedure described above. Mechanical testing of thehydrogel films was conducted in buffered saline on an Instroninstrument, according to modified ASTM D- 1708 test procedure (tensilemodulus) and ASTM D-1938 test procedure (tear strength). Extractibles ofcured films and water content of the hydrogel films were determinedgravimetrically. The results are reported in the following Table.Initiator and Tear Amount Modulus Strength % % Example (wt %) (g/mm²)(g/mm) Extractibles Water  9 I-1800 (1%) 39 18 14.2  38.4 10 I-1800 (2%)48 12 11.2  40.4 11 I-1800 (3%) 41 11 9.0 36.8 12 I-1800 (4%) 47 1014.2  37.9 13 I-1700 (1%) 40 16 12.6  12.6 14 I-819 (0.25%) 48 13 6.337.6 15 I-819 (0.5%) 49 13 7.9 37.6 16 I-819 (0.75%) — 10 9.1 36.3 17I-819 (0.75%)* 36 13 — — 18 I-819 (1%) 48 10 8.2 35.2

[0107] Photo differential scanning calorimetry (Photo DSC)

[0108] Additionally, the curing of various monomer mixtures of Examples9-18 was evaluated using photo differential scanning calorimetry. In aDupont differential scanning calorimetry unit, the monomer mixture isplaced in a sample pan at ambient temperature and polymerized undernitrogen atmosphere by exposure to the light source. The exothermicprofile was monitored, and the following table reports peak time (timeof highest recorded exotherm) and maximum heat flow (at peak time). Forcomparative purposes, 0.5 wt % camphor quinone and 0.5 wt % MDEA wereadded to Mixture 1C (designated CM-1 in the table). The Photo DSCevaluation yielded no recordable peak time, as shown in the table.Initiator and Amount Peak Time Heat Flow Example (wt %) (min) (MW) CM-1CQ/MDEA (0.5%/0.5%) None —  9 I-1800 (1%) 20.6  9 10 I-1800 (2%) 15.3 1311 I-1800 (3%) 12.2 14 12 I-1800 (4%) 11.5 14 13 I-1700 (1%) 21.5  9 14I-819 (0.25%) 17.7 10 15 I-819 (0.5%) 12.8 13 16 I-819 (0.75%) 11.6 1417 I-819 (0.75%)* 14.2 12 18 I-819 (1%) 10.2 17

EXAMPLES 19-27

[0109] As in Examples 9-18, various initiators were added to MonomerMixture 2C, and hydrogel films were cured under a visible light source,processed, and tested for mechanical properties. Photo DSC evaluationwas also undertaken. The results are reported in the following tables.Initiator and Tear Amount Modulus Strength % % Example (wt %) (g/mm²)(g/mm) Extractibles Water 19 I-1800 (1%) 75 6 9.3 27.6 20 I-1800 (2%) 766 10.2  29.3 21 I-1800 (3%) 74 6 11.3  28.1 22 I-1800 (4%) 72 6 14.5 29.6 23 I-819 (0.25%) 79 7 0.9 28.2 24 I-819 (0.5%) 76 7 3.0 28.3 25I-819 (0.75%) 71 7 4.4 28.4 26 I-819 (0.75%)* 75 7 — — 27 I-819 (1%) 767 5.3 28.2

[0110] Initiator and Amount Peak Time Heat Flow Example (wt %) (min)(MW) 19 I-1800 (1%) 3.8 17 20 I-1800 (2%) 2.6 23 21 I-1800 (3%) 2.2 2522 I-1800 (4%) 2.4 29 23 I-819 (0.25%) 3.3 25 24 I-819 (0.5%) 3.0 28 25I-819 (0.75%) 2.0 37 26 I-819 (0.75%)* 2.6 28 27 I-819 (1%) 2.0 38

EXAMPLES 28-31

[0111] Preparation of additional monomer mixtures

[0112] Monomer mixtures, suitable for providing silicone hydrogelcontact lenses, were prepared by mixing ID3S4H, TRIS and DMA.Additionally, IMVT was added at 150 ppm, UVAgent was added at 0.5 pbw,and Irgacure-819 initiator was added at 0.5 pbw. These mixtures aredesignated Monomer Mixture 3A hereafter.

[0113] Monomer mixtures, suitable for providing hydrogel contact lenses,were prepared from 2-hydroxyethylmethacrylate, N-vinylpyrrolidone,crosslinking monomers and 4-t-butyl-2-hydroxycyclohexylmethacrylate.Additionally, IMVT was added at 150 ppm, UVAgent was added at 0.5 pbw,and Irgacure-819 initiator was added at 0.5 pbw. These mixtures aredesignated Monomer Mixture 4A hereafter.

[0114] The mixtures were exposed to three different light sources, forcuring into films, using the general procedures described above: (1) aUV lamp (4000 μW) providing light mainly below 400 nm; (2) a visiblelight source; and (3) the same visible light source with a UV filterusing a set-up as in Examples 5 and 6. The attempt to cure Mixtures 3Aand 4A under the (1) UV lamp resulted in very curly films indicatinguneven curing. Mixtures 3A and 4A were effectively cured using both the(2) visible light source and (3) the visible light source with a UVfilter; mechanical properties of these films, measured as in Example 9,are listed in the following tables. Film Tear Light Appear- StrengthModulus % % Ex. Mix. Source ance (g/mm) (g/mm²) Extr. Water 28 3AVisible slightly 9 46 13.6 24.7 curly 29 3A Vis + flat 10  47 13.1 25.0UV Filter 30 4A Visible slightly 2 19  9.8 69.5 curly 31 4A Vis + flat 221  9.2 68.3 UV Filter

EXAMPLE 32

[0115] Mixture 4A was used to cast contact lenses. The monomer mixturewas placed on the molding surface of a first plastic mold section,shaped to provide an anterior contact lens surface, and a second plasticmold section having a molding surface shaped to provide a posteriorcontact lens surface was placed on the first mold section, the monomermixture being contained in the mold cavity formed between these twomolding surfaces. This assembly was then subjected to a visible lightsource with UV radiation being filtered out. In one set of tests, thetwo mold sections were then immediately separated, lenses were releasedfrom the mold section, and ultimately equilibrated in borate bufferedsaline. In a second set of tests, the lenses were subjected to a thermalpost-cure before separation from the mold sections and hydration. Bothtest runs resulting in hydrogel contact lenses having good opticalquality, with a water content of 61.0% and 61.3%, respectively, amodulus of 42 and 36 g/mm², respectively, and a tear strength of 2 g/mmfor both tests.

[0116] Many other modifications and variations of the present inventionare possible to the skilled practitioner in the field in light of theteachings herein. It is therefore understood that, within the scope ofthe claims, the present invention can be practiced other than asspecifically described.

I claim:
 1. A method for polymerizing a monomer mixture to form a lenscomprising: charging to a mold a monomer mixture including lens-formingmonomers, a UV-absorbing compound and a tinting agent; and exposing themonomer mixture in the mold to a light source including light in thevisible region of the spectrum.
 2. The method of claim 1 , wherein themonomer mixture includes a polymerization initiator including aphosphine oxide moiety.
 3. The method of claim 2 , wherein the initiatorincludes a compound of the general formula:

wherein ar and ar′ are independently an optionally substituted aromaticradical, r is an optionally substituted alkyl or aromatic radical, and nis zero or one.
 4. The method of claim 3 , wherein n is one.
 5. Themethod of claim 3 , wherein the initiator includes a compound selectedfrom the group consisting of:bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; andbis(2,4,6-trimethylbenzoyl) phenylphosphine oxide.
 6. The method ofclaim 1 , wherein the monomer mixture is exposed to light predominantlyin the visible region of the spectrum.
 7. The method of claim 6 ,wherein UV light is filtered from the light source impinging on themonomer mixture.
 8. The method of claim 1 , wherein the lens is acontact lens.
 9. The method of claim 8 , wherein the monomer mixture ispolymerized in a mold cavity formed between a first mold section havinga molding surface shaped to provide a posterior contact lens surface anda second mold section having a molding surface shaped to provide ananterior contact lens surface.
 10. The method of claim 8 , wherein thelens is a hydrogel contact lens.
 11. The method of claim 10 , whereinthe lens is a silicone hydrogel contact lens.
 12. A method forpolymerizing a monomer mixture to form a lens comprising: charging to amold a monomer mixture including lens-forming monomers, a UV-absorbingcompound and a polymerization initiator including a phosphine oxidemoiety; and exposing the monomer mixture in the mold to a light sourceincluding light in the visible region of the spectrum.